1. Field of the Invention
The present invention relates to hydrodynamic torque converters, and more particularly, to a hydrodynamic torque converter having a torsional vibration damper arranged in the inner torus.
2. Description of the Related Art
U.S. Pat. No. 4,043,223 discloses a hydrodynamic torque converter with a converter circuit comprising an impeller wheel, a turbine wheel with a turbine hub, and a stator wheel which together enclose an inner torus in which a torsional vibration damper is arranged. The torsional vibration damper is operably connected with the impeller wheel on one side and with a control disk on the other side. The control disk is connected with an automatic transmission via a first driven shaft so as to be fixed with respect to rotation relative to the automatic transmission. The above-mentioned turbine wheel is connected with a second driven shaft via its turbine hub so as to be fixed with respect to rotation relative to the driven shaft which, similar to the first driven shaft, acts as a transmission input shaft of the automatic transmission which has a clutch for each of the two driven shafts. In defined switching states of these clutches, there is a lockup clutch function by means of which a torque provided by a drive can be transmitted to the transmission while bypassing the converter circuit.
An automatic transmission with two transmission input shafts is referred to in the technical art as a power-dividing transmission. In the transmission according to the '223 patent, there is a first, purely hydrodynamic operating mode in which both clutches are open in the transmission. In the first operating mode, torque received by the drive is transmitted from the impeller wheel via the turbine wheel to the driven shaft associated therewith, and torsional vibrations are damped by the converter circuit. In a second, power-dividing operating mode, however, one of the two clutches is closed and the other is opened, so that a portion of the introduced torque reaches the transmission in the manner described above via the converter circuit, while a second portion of the torque is transmitted from the impeller wheel via the torsional vibration damper and the control disk into the transmission. In a third operating mode/state, the opening and closing states of the two clutches are exchanged compared with the power-dividing operating state and, as a result, the introduced torque is transmitted into the transmission exclusively via the torsional vibration damper and control disk while bypassing the converter circuit. Since the converter circuit is incapable of taking over any vibration-damping function in the third operating state, the torsional vibration damper must compulsorily be connected with the impeller wheel in order to take over this function.
Based on the embodiment of the hydrodynamic torque converter with two driven shafts addressed in the '223 patent, an arrangement of the torsional vibration damper in conventional manner, that is, axially between a drive-side radial flange of the converter housing and the turbine wheel, is generally problematic with respect to design. The problem is that it would then be necessary to axially engage over the turbine hub in order to make a connection between the torsional vibration damper and the associated driven shaft which radially encloses the-driven shaft of the turbine wheel. For this reason, the torsional vibration damper must be arranged in the inner torus of the converter circuit.
Another hydrodynamic torque converter for a power-dividing automatic transmission is shown in DE 35 31 521 A1. The automatic transmission mentioned above (i.e., U.S. Pat. No. 4,023,223) is very complicated in terms of construction and is therefore very expensive, for which reason it is only applied in modern vehicles in isolated cases. On the other hand, hydrodynamic torque converters such as those described, for example, in DE 41 21 586 A1, e.g., in FIG. 1, are used for conventionally constructed automatic transmissions having only one transmission input shaft. In a torque converter of this kind, the piston of a lockup clutch is axially arranged between a drive-side radial flange of the converter housing and the turbine wheel, and is operably connected with the turbine hub via a torsional vibration damper which is disposed axially between the piston and the turbine wheel. Torque that has reached the piston from the radial flange of the converter housing via a friction lining provided at the piston is accordingly conducted via the torsional vibration damper, to the turbine hub and from the turbine hub, due to its tooth engagement with the transmission input shaft, to the transmission input shaft and thus enters into the transmission while bypassing the converter circuit. In a second possible switching state, on the other hand, the torque is conducted via the converter circuit to the turbine hub and the transmission input shaft and enters the transmission.
The simple construction of this torque converter is offset by the following disadvantages: Modern hydrodynamic torque converters must be constructed so as to be extremely narrow axially because the space available in the vehicle for their installation is constantly decreasing. Because of the considerable axial space requirement for the torsional vibration damper between the piston and the turbine wheel, installation space must be saved in that the impeller wheel and turbine wheel and accordingly the converter circuit are increasingly built so as to be narrower in the axial direction. This worsens the flow ratios in the converter circuit and results in a decrease in efficiency. In addition, in order to limit the axial space requirement of the torsional vibration damper, the latter is provided with springs of relatively small diameter. The rigidity of these springs must be correspondingly high, so that the torsional vibration damper can exercise only a limited damping behavior, especially with torsional vibrations of low frequency. This disadvantage can be mitigated in that the torsional vibration damper is placed very far to the radial outside as in DE 44 24 988 A1, but there is also not an optimum damping behavior in this case.